| 摘要 |
PROBLEM TO BE SOLVED: To correspond to a diffraction grating pitch equal to or less than a wavelength of a light source and hereby improve a resolution. SOLUTION: Light from a laser diode 10 is output in a non-vertical direction to a scale 18. An interference fringe is detected by mutually crossing zero dimensional light that incident light is reflected by the scale 18 and diffraction light obtained by diffracting the incident light by the scale 18. The interference fringe can be detected even when a pitch p1 of the diffraction grating of the scale 18 or a pitch p2 of the diffraction grating of an optical path changer 40 is less than a wavelengthλof the light source.
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